A 75.0g sample of liquid contains 17.5% by mass of H3PO4 (molar mass=98.0g/mol). If 215.0mL of Ba(OH)2 is needed to completely neutralized the acid, determine the concentration (or molarity) of the Ba(OH)2 solution used.

Answer 1

2H3PO4 + 3Ba(OH)2 ==> Ba3(PO4)2 + 6H2O
mass H3PO4 in the sample = 75.0 x 0.175 = approx 13 but this is just a close estimate. You need to redo all of these calculations more accurately.
mols H3PO4 = appox 13/98 = 0.13
Using the coefficients in the balanced equation, convert mols H3PO4 used to mols Ba(OH)2 needed. 0.13 mols H3PO4 x (3 mols Ba(OH)2/2 mols H3PO4) = approx 0.2 mols Ba(OH)2
[Ba(OH)2] = mols/L = approx 0.2/0.215 = ?